This invention relates to a method and an apparatus for inspecting a surface shape and pattern of an object, and more particularly to a method and an apparatus for inspecting a three-dimensional shape and pattern of the surface of an object.
As examples of an apparatus for inspecting a three-dimensional shape and pattern of the surface of an object, apparatuses for inspecting the soldered condition of an electronic part after the electronic part has been mounted on a board are described in JP-A-61-293657 (literature (1)), and "A Tiered-Color Illumination Approach for Machine Inspection of Solder Joints", David W. Capson and Sai-Kit Eng, IEEE Transactions on Pattern Analysis and Machine Intelligence, Vol 10, No. 3, May 1988, pp. 387-393 (literature (2)).
In the literature (1), a solder joint under inspection is illuminated sequentially from a plurality of angles, the features such as shapes of highlight produced by regular reflection of illumination are extracted in binary form from the images obtained by illumination from the different angles, and the solder joint is judged as to whether or not it is acceptable from a total assessment of the features obtained from the respective images. To switch over illumination from the plurality of angles, a shutter mechanism is used or monochrome LEDs which can be switched at high speed are used.
In literature (2), the solder joint is illuminated by two high-angle and low-angle lights of different emission frequencies, and from images obtained by illumination from different angles, the solder joint is judged whether it is acceptable or not.